In the aftermath of automotive and aircraft crashes, occupants are frequently trapped inside deformed metal structures which are too strong merely to be pulled to one side. Instead, portions of these structures must be removed or strongly bent to enable the occupants to be rescued.
Because very large forces are required for this purpose, it is common to use devices powered by pressurized hydraulic fluid as an energy source. Such a system must include an engine, a pump, a reservoir, and connecting hoses and fittings. All of these are weighty and cumbersome. They complicate the use of the device, and require considerable maintenance. Their life between overhauls is limited by their seals. They do provide the advantage that they can be used either as a spreader to spread portions of the structure apart, or to pull them together, although the former is nearly always preferred.
As to maintenance and life between overhauls, it is instructive to learn that these devices are used many more times in training exercises than they are in rescues. It is not uncommon for a device to be used in training or demonstrations one hundred times, and in rescues only a few times. Frequently, the uses in training will wear out the tool before it is used in an emergency. Obviously hydraulic tools have substantial inherent disadvantages.
If structure is merely to be spread apart by bending it, a steady separative force such as can be exerted by a hydraulically actuated tool is useful, and for that action is sometimes preferred to a percussive force. However, this requires considerable repositioning of the tool and multiple passes with it. This is clumsy and time-consuming when time cannot be affordable. As a consequence, cutting has frequently been suggested as an alternative, so that interfering structure can quickly be removed. Power saws can be used in a cutting mode such as by a rotary saw when there is no fire or explosion risk, but these also require a motor means such as a piston engine or an electrical generator, again an inconvenience or worse.
Another conventional method to remove interfering metal is to chop it away. Firemen have used axes for this purpose for decades. When it is tolerable, it is often preferred for its quickness, because an abrupt high-unit loading chopping force is considerably more effective than bending or sawing. Still, with persons trapped inside only inches away, strong unreacted chopping forces such as are exerted by axes, can rarely be tolerated.
It is an object of this invention to provide a chopping-type rescue tool whose power is totally self-contained, and which exerts its cutting force in a closed system wherein much, even most, of the impact shock is reacted by the body of the tool and by the structure being cut.
It is another object of this invention to provide a tool which can be actuated without contact with a structure to be cut in the sense of being fired "in the air", without causing damage to the tool or to anything surrounding it.
It is yet another object to provide such a tool with gas generating means which exerts a rapidly peaking high gas pressure to drive a chopping blade.